The present invention relates to a multiplex communication system based on a loop transmission and, more particularly, to a multiplex communication system which is suitable for realizing a concentrated or intensive wiring in a motor vehicle.
As an attempt to realize a concentrated or intensive wiring by multiplexing data transmission in a motor vehicle, there has been heretofore proposed a multiplex communication system in which optical fiber inherently less susceptible to noise is employed for constituting transmission line or path. As a typical one of such system, there may be mentioned a double-loop transmission or communication system implemented by using optical fiber.
The double-loop transmission system can certainly assure a high reliability of data transmission. However, since each of transmitter units requires four photoelectric converters, difficulty is encountered in miniaturization of the transmitter unit. Further, all the photoelectric converters belonging to either one or other of the double loop optical fiber transmission paths have to be operated simultaneously in the course of data transmission, involving thus a relatively large power consumption. As a consequence, when the double loop transmission system employed in a motor vehicle is continuously operated for a long time with the engine of the vehicle being stopped, there may arise such undesirable situation that an onboard battery is exhausted, giving rise to a problem.
An example of the double loop transmission system of this kind is disclosed, for example, in Japanese Patent Application Laid-Open No. 92948/1982.